Given data:
Alvin paddled for 2 hours with a 7-km/h current to reach a campsite.
The return trip against the same current took 9 hours.
Let Boat speed speed x km/h.
The current speed 7 km/h.
The against current x- 7.
The with current x+ 7.
The time paddles against current 9 hours.
The time paddles with the current is 7 hours.
The Distance is same here,
[tex]Distance=speed\cdot\text{time}[/tex]thus,
[tex]\begin{gathered} 9(x-7)=7(x+7) \\ 9x-63=7x+49 \\ 9x-7x=49+63 \\ 2x=112 \\ x=\frac{112}{2} \\ x=56 \end{gathered}[/tex]Thus, the speed of the boat in still water is 56 km/h.
